G protein beta 3 gene: structure, promoter, and additional polymorphisms.
Recent studies have shown that a polymorphism (C825T) in the gene encoding the G protein beta 3 subunit (GNB3) is associated with hypertension and obesity. We characterized the entire GNB3 gene, which spans 7.5 kb and is composed of 11 exons and 10 introns. Its promoter lacks a TATA box but harbors GC-rich regions. The functional activity of the GNB3 promoter was verified with reporter gene assays that also demonstrated its inducibility by phorbol esters. A novel polymorphism in the promoter region A(-350)G occurred with frequencies (G allele) of 76%, 97%, and 61% in Africans, Chinese, and Germans, respectively. Reporter gene constructs with either the A or the G allele did not differ with regard to inducement of the reporter protein. A silent nucleotide exchange in the coding region (A657T) occurred with T allele frequencies ranging from 0.5% to 2.4%. Another polymorphism (G814A) results in the replacement of glycine by serine at position 272. In Germans, the A allele occurred at a frequency of 10%. Finally, a C1429T polymorphism in the 3' untranslated region of GNB3 was identified that occurred at T allele frequencies of 38%, 17%, and 30% in Africans, Chinese, and Germans, respectively. Haplotype prediction indicated in Germans an almost complete association of GNB3 825T with 1429T, and vice versa. An analysis of these polymorphic loci in nonhuman primates revealed that the ancestral GNB3 gene harbored the (-350)G, 825C, and 1429C alleles. This is the first complete characterization of the human GNB3 gene and its promoter region, which will enable refined epidemiological and biochemical investigations of GNB3 in hypertension and obesity.